1. Field of the Invention
The present invention relates to a system for optically and electronically ascertaining the rate of precipitation in ambient air using an unattended instrument.
2. Description of the Prior Art
At present, precipitation rates are conventionally measured by utilizing tipping bucket rain gauges. In such systems a small bucket is exposed to ambient air. When precipitation occurs rain water or melted snow collects in the bucket. When a sufficient amount of precipitation has been collected in the bucket, the bucket will tip, thereby emptying its contents, and triggering a counter. A second bucket is then immediately reset to an upright position to again receive further precipitation. The frequency with which the bucket tips and empties its contents is indicative of the rate of precipitation.
One significant problem in conventional precipitation gauges is that the accuracy of such gauges is quite poor at extremely heavy and extremely light precipitation rates. When precipitation is extremely heavy a significant inaccuracy results due to the time required to mechanically reset the bucket. Conventional tipping bucket rain gauges likewise suffer from considerable inaccuracy at lower precipitation rates due to the evaporation problem and the relatively long resolution time required.
The purpose of providing automated rain gauge measuring systems is to provide for remote monitoring of weather without the necessity for human observation at a site where weather is to be monitored. Automated precipitation rate monitoring allows precipitation conditions at unmanned airfields to be remotely monitored and reported to aircraft in flight.
Automatic rain gauge systems have also been devised which employ laser scintillations and scattering. Such conventional optical rain gauges have utilized optical transmitters employing sources of coherent light, typically laser beams. The spatial separation between the receiver and the transmitter of a conventional laser scintillation detection system is on the order of fifty meters. This large spatial separation between the transmitter and the receiver of an optical rain gauge employing a laser is inconvenient for use in field operation, such as at airports, due to the large area which is required to effectuate automated operation. The ground movement caused by frost or water may also induce pointing problems of the laser beam. Furthermore, such conventional systems are subject to considerable contamination as a result of air turbulence which is likely to occur in ambient air over a distance of fifty meters. As a result, optical rain gauges employing lasers have been utilized to only a very limited degree.